Retrospective data analyses have suggested that carbonic anhydrase IX (CAIX) may have a predictive role in patients with metastatic clear cell renal cell carcinoma (ccRCC) receiving high dose interleukin-2 or sorafenib. We examined the predictive value of CAIX in estimating treatment outcome in patients receiving sorafenib vs. placebo as part of the Treatment Approaches in Renal Cancer Global Evaluation Trial (TARGET) study.Paraffin embedded tumor tissues were collected from 133 patients from the TARGET study (n = 903). The percentage of CAIX-positive cells was assessed by a single pathologist. The impact of CAIX expression on progression-free survival (PFS, primary endpoint) and tumor shrinkage (TS, secondary endpoint) was analyzed.Clinical characteristics were similarly distributed between patients with low vs. high CAIX staining, as well as patients with available CAIX data vs. not. Median PFS for patients with high CAIX vs. low CAIX expression was 5.5 and 5.4 months, respectively, on the sorafenib arm (P = 0.97), and 1.5 and 1.7 months on the placebo arm (P = 0.76). Median TS for patients with high CAIX status was -14.9% vs. -12.6% in patients with low CAIX status (P = 0.63) on the sorafenib arm, and +1.3% (high CAIX) vs. +4.8% (low CAIX) in patients on the placebo arm (P = 0.60).Despite suggestive retrospective evidence, data from the TARGET study did not find CAIX expression status to be either predictive of clinical benefit for treatment with sorafenib or of prognostic value in patients with metastatic ccRCC following cytokine therapy.